The present invention relates to silver salt photothermographic dry imaging materials (hereinafter, also denoted simply as photothermographic materials or light sensitive materials), and an image recording method-and image forming method by the use thereof.
In the field of graphic arts and medical treatment, there have been concerns in processing of photographic film with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. There has been desired a photothermographic material for photographic use, capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter.
Known as such a technique is a thermally developable photothermographic material which comprises on a support an aliphatic carboxylic acid silver salt, light sensitive silver halide grains, and reducing agent, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. Morgan, xe2x80x9cDry Silver Photographic Materialsxe2x80x9d (Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991). In such photothermographic materials, no solution type processing chemicals is used, providing a simple and environment friendly system to users.
There was proposed a photothermographic material containing compounds, so-called a contrast-increasing agent or silver-saving agent, thereby achieving higher densities based on silver coverage per unit area, compared to photothermographic materials not containing such compounds.
Such photothermographic materials are described in U.S. Pat. Nos. 5,496,695, 5,545,505, 5,545,507, 5,637,449, 5,654,130, 5,635,339, 5,545,515, 5,686,228; JP-A Nos. 10-339929, 11-84576, 11-95365, 11-95366, 11-109546, 11-119372, 11-119373, 2000-356834 and 2001-27790 (hereinafter, the term, JP-A is referred to as unexamined Japanese Patent Application publication), in which a various kinds of contrast-increasing agents and silver-saving agents were proposed.
However, problems arose with photothermographic materials containing such a silver-saving agent that, depending of pre-exposure storage conditions, densities in unexposed areas are different after being processed and an intended density (for example, maximum density) could not be achieved. Furthermore, there were problems involved in fogging.
The present invention was realized in light of the foregoing problems. Thus, it is an object of the invention to a silver salt photothermographic dry imaging material exhibiting an enhanced maximum density (Dmax), reduced fogging and superior storage stability, and an image recording method and image forming method by use thereof.
The foregoing object of the invention can be accomplished by the following constitution:
1. A silver salt photothermographic imaging material comprising a light-insensitive aliphatic carboxylic acid silver salt, a light-sensitive emulsion containing light-sensitive silver halide, a reducing agent for silver ions, a binder and one or more cross-linking agents, wherein at least one of the cross-linking agents is an aromatic polyisocyanate compound and the photothermographic material further comprises a compound selected from compounds represented by the following formulas (1) through (3): 
xe2x80x83wherein R11, R12 and R13 are each a hydrogen atom or a univalent substituent; X11 is an electron-donating heterocyclic group, a cycloalkyloxy group, a cycloalkylthio group, a cycloalkylamino group or cycloalkenyl group; 
xe2x80x83wherein R21 is an alkyl group; R22 and R23 are each a hydrogen atom or a univalent substituent; X21 is an electron-withdrawing group; L21 is an aromatic carbon-ring group; and n2 is 0 or 1; 
xe2x80x83wherein X31 is an electron-withdrawing heterocyclic moiety, a halogen atom or a haloalkyl group; one of R31 and R32 is a hydrogen atom and the other one is a hydroxy group.
2. The photothermographic imaging material described in 1., wherein R11 of formula (1) is an electron-withdrawing group;
3. The photothermographic imaging material described in 1. or 2, wherein R11 in formula (1) and X21 in formula (2) are a cyano group;
4. The photothermographic imaging material described in any of 1. through 3, wherein one of R12 and R13, or R22 and R23 is a hydrogen atom and the other one is an electron-donating group;
5. The photothermographic imaging material described in any of 1. through 4., wherein the aromatic polyisocyanate compound is represented by formula (Z):
(X2xe2x95x90Cxe2x95x90Nxe2x80x94J1)v2xe2x80x94Lxe2x80x94[J1xe2x80x94(Nxe2x95x90Cxe2x95x90X2)v1]nxe2x80x83xe2x80x83formula (Z)
xe2x80x83wherein J1 is a substituted or unsubstituted arylene group, or a substituted or unsubstituted heterocyclic group; L is a polyvalent linkage group derived from a substituted or unsubstituted alkyl, alkenyl, aryl or heterocyclic group, or a linkage group formed by linking these groups through a bond or a linking group; X2 is an oxygen atom or a sulfur atom; v1 is an integer of 1 or more, v2 is 0 or an integer of 1 or more, and n is an integer of 1 or more, provided that when v2 is 0, v1 or n is an integer of 2 or more.
6. The photothermographic imaging material described in any of 1. through 5., wherein the light-insensitive aliphatic carboxylic acid silver salt is one which is formed in the presence of a compound capable of functioning as a crystal growth-retarding agent or a dispersing agent;
7. The photothermographic imaging material described in 6, wherein the crystal growth-retarding agent or a dispersing agent contains a hydroxy or carboxy group;
8. An image recording method, wherein the photothermographic material described in any of 1 through 7 is exposed by using a laser exposure apparatus, in which scanning laser light is not exposed at an angle substantially vertical to the exposed surface of the photosensitive material;
9. An image recording method, wherein the photothermographic material described in any of 1 through 7 is exposed by using a laser exposure apparatus, in which scanning laser light is longitudinally multiple.
10. An image recording method, wherein scanning exposure is performed onto the photothermographic material described in any of 1. through 7. using at least two laser beams to record images;
11. The image recording method described in any of 8 through 10, wherein the laser beams used in the scanning exposure are one of 600 to 1200 nm wavelength;
12. An image forming method, wherein the photothermographic material described in any of 1 through 7 is processed at a temperature of 100 to 150xc2x0 C.;
In this invention, it was discovered that incorporation of at least one of the foregoing compounds represented by formulas (1) through (3) leads to a photothermographic material exhibiting enhanced sensitivity, higher maximum density (Dmax), superior storage stability and higher contrast. It was further discovered that the use of hydrazine derivatives represented by (H-1) or (H-2) in JP-A 2001-174945, in combination with the foregoing compounds led to further enhanced effects of the invention.